Chlorination has long been considered as a means for recovering metal values from ores, scrap and other material. An example is the commercial process for recovering titanium. This process is practical because the chloride, titanium tetrachloride, is a liquid at room temperature and a gas at a 136.degree. C. This is in contrast to most other metal chlorides which melt at high temperatures which makes them difficult to chlorinate by direct chlorination under ambient conditions. Because of the high melting point of these chlorides they form an impervious surface on the particles being chlorinated which prevents the chlorination reaction from going to completion. Another difficulty is that the chlorides formed sometimes form viscous liquids which inhibit movement in the fluid beds frequently used in chlorination and which again result in incomplete reaction.
Another major difficulty in producing the high melting point chlorides is that, except in a case where the metal chloride can be removed because it is volatile, the separation of one metal chloride from another is a difficult and expensive procedure. Thus, it has been necessary to dissolve the chlorides formed in water to perform separations and purification and this involves substantial expense. Although chlorination of most metals has been demonstrated in the laboratory, it has not been practical commercially for the reasons set forth above.
Iron is an example of a metal which cannot be economically recovered from its ore by present chlorination procedures. This metal is frequently encountered in nature either as an impurity in valuable materials or as a material of value which contains impurities which must be removed in order for the iron to be useful. In processing iron ores or iron-containing materials, chlorination has been suggested as a process route. Thus, in U.S. Pat. No. 2,895,796 a process is disclosed directed to recovering iron from pyrite in which the latter is chlorinated to ferrous chloride and sulfur under ambient conditions. The chlorination is conducted in the presence of a liquid solvent of chlorine. Examples show the use of sulfur and sulfur monochloride as such solvents. While this process shows a means for producing ferrous chloride, it does not disclose a practical method for separation of the iron materials from other materials.
In U.S. Pat. No. 3,652,219 a process is also disclosed wherein pyrite is reacted with sulfur chloride in an excess of sulfur chloride to form ferrous chloride. The patentee then chlorinates the iron to ferric chloride which he separates by distillation and then oxidzes the iron to iron oxide. This somewhat overcomes the disadvantage of the process of U.S. Pat. No. 2,895,796, but by an expensive and difficult route, i.e., the distillation and subsequent oxidation of ferric chloride. The process of U.S. Pat. No. 3,652,219 has a further disadvantage of causing the formation of noxious sulfur monochloride.
Processes other than chlorination have been attempted for processing iron from its ores in scrap, and the removal of iron contamination from other valuable materials, as this field is one of the major areas of industrial inorganic chemistry. As respects aqueous systems, it is known to dissolve iron in mineral acids and, after separation from unwanted impurities or from valuable products, to precipitate the iron as an oxide or hydrated oxide. In the aqueous system difficulties can be encountered in terms of difficult-to-filter precipitates and coprecipitation. In the case of sulfur-containing material it is difficult to convert all the sulfur to elemental sulfur in the presence of water. A part of the sulfur is inevitably becoming unwanted sulfate as the process proceeds.
When the metal to be recovered is present in nature as its sulfide, as in the case of iron, zinc and other metals, the recovery problem is compounded by the pollution problem and conformance with environmental clean air regulations. In the present commercial methods for treating sulfide ores and concentrates, the general practice involves smelting or roasting the sulfides through a complex series of operations which drive off the sulfur as sulfur dioxide. The metal values are effectively recovered by these operations. However, large volumes of sulfur dioxide are produced which are not always conveniently recovered so that serious air pollution results. As a substitute, hydrometallurgical processes, which convert the sulfide to elemental sulfur with recovery of the corresponding metal, are being extensively developed. Examples of such processes are those described in U.S. Pat. Nos. 3,673,061; 3,736,238 and 3,766,926, which describe effective process for electrolytic dissolution of sulfide concentrates. Chemical leaching processes as a substitute for the hydrometallurgical processes are described in U.S. Pat. No. 3,767,543 and U.S. Bureau of Mines Report on Investigations 7474.
A major difficulty with the present hydrometallurgical processes is that it is not practically possible to convert all the sulfide sulfur to elemental sulfur. A part of the sulfur is inevitably converted to sulfate which constitutes a waste of energy and a disposal problem. Further, the sulfur is finely divided and intermixed with gangue so that special processes are required for its economic recovery. Also, it is not possible with presently available hydrometallurgical processes to work at very high concentrations of valuable metal, so that large volumes of solutions must be heated, cooled, pumped, and processed.
Accordingly, it is the principal object of this invention to provide a process for the chlorination of metals from their compounds which is a substantially pollution-free process, which is free of the problem of formation of high melting chlorides which coat particles of the compound, which avoids the formation of a sticky liquid sulfur, and which obviates other problems of the prior art processes for recovery of metals from the ores.